Re: [HACKERS] How does postgres store the join predicate for arelation in a given query

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От Gourav Kumar
Тема Re: [HACKERS] How does postgres store the join predicate for arelation in a given query
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Msg-id CAPzqDmi5qD4XG=ERj_R4U=AjsoZf5HxEzzUMaaCiZggh_H_HJg@mail.gmail.com
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Ответ на Re: [HACKERS] How does postgres store the join predicate for arelation in a given query  (Gourav Kumar <gourav1905@gmail.com>)
Ответы Re: [HACKERS] How does postgres store the join predicate for arelation in a given query
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Why does have_relevant_joinclause() and have_relevant_eclass_joinclause() return true for all possible joins for the query given below.
Even when they have no join predicate between them.
e.g. join between ss1 & ws3, ss2 & ws3 etc.

The query is :
TPC-DS query 50

 -- query 50 in stream 0 using template query31.tpl
with ss as
 (select ca_county,d_qoy, d_year,sum(ss_ext_sales_price) as store_sales
 from store_sales,date_dim,customer_address
 where ss_sold_date_sk = d_date_sk
  and ss_addr_sk=ca_address_sk
 group by ca_county,d_qoy, d_year),
 ws as
 (select ca_county,d_qoy, d_year,sum(ws_ext_sales_price) as web_sales
 from web_sales,date_dim,customer_address
 where ws_sold_date_sk = d_date_sk
  and ws_bill_addr_sk=ca_address_sk
 group by ca_county,d_qoy, d_year)
 select /* tt */
        ss1.ca_county
       ,ss1.d_year
       ,ws2.web_sales/ws1.web_sales web_q1_q2_increase
       ,ss2.store_sales/ss1.store_sales store_q1_q2_increase
       ,ws3.web_sales/ws2.web_sales web_q2_q3_increase
       ,ss3.store_sales/ss2.store_sales store_q2_q3_increase
 from
        ss ss1
       ,ss ss2
       ,ss ss3
       ,ws ws1
       ,ws ws2
       ,ws ws3
 where
    ss1.d_qoy = 1
    and ss1.d_year = 2000
    and ss1.ca_county = ss2.ca_county
    and ss2.d_qoy = 2
    and ss2.d_year = 2000
 and ss2.ca_county = ss3.ca_county
    and ss3.d_qoy = 3
    and ss3.d_year = 2000
    and ss1.ca_county = ws1.ca_county
    and ws1.d_qoy = 1
    and ws1.d_year = 2000
    and ws1.ca_county = ws2.ca_county
    and ws2.d_qoy = 2
    and ws2.d_year = 2000
    and ws1.ca_county = ws3.ca_county
    and ws3.d_qoy = 3
    and ws3.d_year =2000
    and case when ws1.web_sales > 0 then ws2.web_sales/ws1.web_sales else null end 
       > case when ss1.store_sales > 0 then ss2.store_sales/ss1.store_sales else null end
    and case when ws2.web_sales > 0 then ws3.web_sales/ws2.web_sales else null end
       > case when ss2.store_sales > 0 then ss3.store_sales/ss2.store_sales else null end
 order by web_q2_q3_increase;

-- end 


On 13 October 2017 at 01:00, Gourav Kumar <gourav1905@gmail.com> wrote:
Well for this given query it is possible. I haven't come across any such query yet.

Possibly because I am more concerned about the TPCDS and TPCH benchmarks, where it's less likely to occur.

On 13 October 2017 at 00:52, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Gourav Kumar <gourav1905@gmail.com> writes:
> A Join clause/predicate will only mention 2 relations. It can't have 3 or
> more relations.

Really?  What of, say,

        select ... from a,b,c where (a.x + b.y) = c.z;

                        regards, tom lane



--
Thanks,
Gourav Kumar
Computer Science and Automation
Indian Institute of Science



--
Thanks,
Gourav Kumar
Computer Science and Automation
Indian Institute of Science

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